Prepregs containing woven or non-woven glass fabrics as a substrate are generally prepared by impregnating such fabrics with thermosetting resins and B-staging the impregnated systems (namely, a semi-cured state that, upon heating, the systems once melt and then heat-cure). In most cases, the prepregs are used in the manufacture of laminates, copper-clad laminates, multilayer printed wiring boards, and the like after cutting the same into predetermined sizes.
Cutting of B-staged, resin-impregnated substrates (prepregs) in continuous form into predetermined sizes has conventionally been conducted by means of rotary cutters or shearing cutters at ordinary temperature, with the single prepreg being cut at a time or with a plurality of prepregs being superposed and cut simultaneously. In this cutting method, the glass fiber substrate at the cut edges is partly broken into powder, while the semi-cured matrix resin at the cut edges is also broken into powder over the area ranging from the cut edges to about 0.5 to 2 mm inside the edges. If the cut prepregs in such a state are, as they are, transported and combined to produce laminates or other products, the glass and resin powder particles generated are not only scattered in the air to impair the working atmosphere, but fall as foreign matter on laminates or other products to be manufactured during the laminating step.
In order to eliminate these problems, it has been proposed to heat the edges of a cut prepreg to a temperature not lower than the softening point of the matrix resin but not higher than the hardening temperature of the resin by means of infrared rays, hot air, hot platens, or the like, to thereby melt the edges as disclosed in, for example, JP-A-63-158216 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). It has also been proposed to cut off the edges of a cut prepreg after the edges are heated to a temperature not lower than the softening point of the matrix resin but not higher than the hardening temperature of the resin, by means of infrared rays, hot air, hot platens, or the like as disclosed in, for example, JP-A-63-158217. However, the former method is disadvantageous in that heating to the softening point (the melting initiation temperature or melting temperature) or a higher temperature needs relatively much time, and that because the heating temperature is too high, the heated parts of the prepreg are changed in property and become to have tackiness to disadvantageously adhere to other substances. The latter method is also disadvantageous in that the melted or softened resin tends to adhere to the cutter blade during cutting and the resin adhered to the blade should be removed for smooth cutting. Furthermore, both methods are disadvantageous in that since the temperature of the matrix resin of the prepreg is raised to the softening point of the resin or a higher temperature, the curing properties of the matrix resin are changed.